The size of natural atoms, d, is always small compared to the wavelength, λ, of the radiation that they are interacting with. This allows to make the dipolar approximation which simplifiers the theoretical description of the atom. Most artificial atoms are also small. However, if an artificial atom is placed on a piezoelectric surface the atom can be made to interact with sound in the form of Surface Acoustic Waves (SAW). In this case, the limit of a "large atom" where d > λ can be reached because of the slow propagation speed of sound, v. This allows us to put an antenna on the atom such that the emission from the atom can be tailored both spatially and in frequency. It is also possible to go one step further and create a "giant atom" where the time it takes for an excitation to pass the atom, d/v is larger than the relaxation time, τ, of the atom. It can be shown that an atom that satisfies the giant atom criterion automatically also satisfies the large atom criterion. In the giant atom case an excitation emitted from the atom has a finite probability of being reabsorbed by the atom, leading to nonexponential decay of the atom. In this talk I will describe experiments demonstrating properties such giant atoms.
[1] G. Andersson, B. Suri, L. Guo, T. Aref and Per Delsing, "Non-exponential decay of a giant artificial atom," Nature Physics 15, 1123 (2019)
Heavily used in classical signal processing, surface acoustic waves (SAWs) have also been proposed as a means to coherently couple distant solid-state quantum systems. Several groups have already reported the coherent coupling of standing SAWs modes to superconducting qubits, opening the door to the control and detection of quantum phonon states. In this talk, I will describe our recent progress in coupling superconducting qubits to propagating SAWs. We can controllably release and capture individual itinerant photons, demonstrating quantum state transfer as well as remote entanglement generation between superconducting qubits using phonons. Going a step further, I will show how two-phonon entanglement can be generated and used to realize a fundamental quantum optics experiment, quantum erasure, also using phonons.
By adapting the tools of circuit quantum electrodynamics (cQED), the field of circuit quantum acoustodynamics (cQAD) aims to further our ability to create, control, and measure the quantum states of mechanical motion. Since mechanical resonators have drastically different properties from their electromagnetic counterparts, they could potentially be used to make new circuit elements for storing, processing, and transducing quantum information. I will present a summary of the progress in realizing cQAD systems based on bulk acoustic wave resonators, including our recent work on improving the properties of these devices in order to access a greater range of protocols for quantum control of mechanical motion.
The transduction of quantum microwave signals to optical photons would enable a new form of long range entanglement distribution between superconducting quantum circuit nodes. Mechanical transducers of various forms are currently being explored for quantum microwave-to-optical transduction, with key figures of merit being transducer efficiency and added noise. In this presentation I will describe recent work at Caltech to realize an integrated piezo-acoustic-based transducer for direct coupling of a transmon qubit with an optomechanical cavity. While added noise of approximately 0.5 quanta was obtained in this transducer design, significant improvements in the internal and external efficiency, as well as the repetition rate are required to perform remote entanglement between superconducting nodes over an optical channel. I will discuss our current work to address these limitations.
The use of phonons as quantum coherent carriers of information brings many potential advantages in the context of quantum computation, storage, and sensing, and has spurred a renaissance of phonon physics and device technologies. However, the utilization of phonons for quantum technologies also raises a myriad of fundamental questions surrounding phonon coherence in quantum phononic media. To tackle these challenging questions, we present a versatile new strategy for both phonon spectroscopy and quantum experimentation that utilizes Brillouin interactions to access high frequency bulk acoustic phonon modes within practically any transparent medium. Using cavity optomechanical techniques to radically enhance Brillouin-based coupling to bulk acoustic phonons within crystalline media, we show that one can readily increase coupling rates to permit the generation and detection of individual quanta of sound for quantum experimentation or spectroscopy within macroscopic substrates. Making simple modifications to crystalline surfaces, we also create phononic resonators with ultra-long lived bulk acoustic phonon modes that are readily accessible with light. Combining these features with piezoelectric coupling, these same devices and techniques open the door to new hybrid electro-optomechanical and superconducting qubit technologies with an array of compelling features.
The ability to coherently interconvert microwave and optical signals at the level of individual photons is an outstanding scientific and technological challenge of particular relevance to quantum computing and future quantum networks. Numerous groups are pursuing device architectures involving either mechanical systems as intermediaries or direct electro-optic transduction via the Pockels effect. I will present two non-standard material systems - gallium phosphide and barium titanate - that offer promising alternative platforms for such devices, including fabrication methods and early results towards demonstrating coherent microwave-optical transduction.
Mechanical systems have recently attracted significant attention for their potential use in quantum information processing tasks, for example, as compact quantum memories or as transducers between different types of quantum systems. Early experiments included ground-state cooling of the mechanical motion and squeezing of the optical field. Recent advances have allowed to perform measurements which realize various mechanical quantum states.
Here, we would like to discuss several experiments where we demonstrate non-classical behavior of mechanical motion by coupling a micro-fabricated acoustic resonator to single optical photons. Our approach is based on optomechanical crystals, which possess engineered mechanical resonances in the Gigahertz regime that can be addressed optically from the conventional telecom band. Our measurements establish quantum control over acoustic motion, including the heralded generation and on-demand readout of single phononic excitations. We further demonstrate high quality light-matter entanglement as well as heralded entanglement between two mechanical modes employing quantum optics protocols. These results are a promising step towards using such devices for quantum information processing tasks and testing quantum physics with massive objects.
In this talk I will outline our recent progress on quantum phononic devices fabricated from lithium niobate. I will outline the design of structures that can control the propagation and coupling of mechanical waves, as well as our current understanding of sources of dissipation in these devices. Finally, I will talk about prospects of these devices for quantum computing and transduction.
Mechanical resonators based on carbon nanotubes feature a series of truly exceptional properties. In particular, the mechanical vibrations are highly sensitive to the tiny forces associated with the electron states in the nanotube and vice versa, leading to large backaction effects. In this talk, I will present results where we strongly couple mechanical vibrations to the two electron states involved in single-electron tunnelling (SET). It renormalizes the resonance frequency by a large amount, up to 25% of its value. This results in a highly nonlinear potential for mechanical vibrations despite the relatively low quanta population (about 80 quanta).
1US Naval Research Laboratory, Washington DC 20375; 2NRC Postdoctoral Fellow at Naval Research Laboratory, Washington DC 20375; 3Department of Physics, University of Antwerp-B2020, Antwerp, Belgium; 4Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831
* Equal contributions.
Two-dimensional (2D) materials enable engineering of the ultrafast spatiotemporal response of composite nanomechanical structures. In this talk, we will describe high frequency, high quality factor (Q) 2D acoustic cavities operating in the 50-600 GHz frequency (f) range with f x Q products up to 1x10^14. Cavity functionality is expanded by heterogeneities (steps and interfaces), as demonstrated through implementing coupled cavities and frequency-comb generators. We will describe energy dissipation measurements in 2D cavities and compare them with attenuation derived from phonon-phonon scattering rates calculated using a fully microscopic ab initio approach. Phonon lifetime calculations extended to low frequencies (< 1 THz) and combined with sound propagation analysis in ultrathin plates provide a framework for designing acoustic cavities that approach their fundamental performance limit.
Doubly-clamped pre-stressed silicon nitride string resonators excel as high Q nanomechanical systems enabling room temperature quality factors of several 100,000 in the 10 MHz eigenfrequency range. They represent an ideal testbed to explore the nonlinear dynamics of a strongly driven nanostring. The focus of this presentation will be on the one- and two-tone spectroscopy of the driven string. In both cases, a pair of well-resolved satellite peaks allows to characterize squeezing in the thermal regime without the need to perform a homodyne measurement [1,2]. Unlike the information extracted from the power spectrum of the driven resonator, the analysis of the satellite peaks in the response spectrum of the driven resonator to a weak probe equally applies to squeezing in the quantum domain. In addition, the response to the probe reveals resonant absorption as well as resonant amplification of the probe field [2].
[1] J. S. Huber, G. Rastelli, M. J. Seitner, J. Kölbl, W. Belzig, M. I. Dykman, and E. M. Weig, "Spectral evidence of squeezing of a weakly damped driven nanomechanical mode", Phys. Rev. X 10, 021066 (2020)
[2] J. S. Ochs (née Huber), M. J. Seitner, M. I. Dykman, E. M. Weig, "Amplification and spectral evidence of squeezing in the response of a strongly driven nanoresonator to a probe field", Phys. Rev. A 103, 013506 (2021)
We will summarize our results on thermal transport in ultrathin free-standing silicon and nano-crystalline silicon nanomembranes and phononic crystals from the perspective to understand and control thermal dissipation. We will report our findings in 1- and 2-optomechanical Si nanobeam at room temperature. In the former case we will gather the findings on mechanical lasing, locking to an external reference and chaos. In the latter case we will summarise our results on, e.g, selective mechanical coupling and locking to and external reference as well as the interplay between a leader and a follower nanobeam leading to synchronization [1]. We will show how the phase noise can be decreased and how the locking mechanisms enhances the robustness of mechanical lasing [2]. We will discuss an approach on the estimation of thermal dissipation connecting the Q-factor to the thermal conductivity, otherwise cumbersome to obtain in these complex structures, and the replacement of SOI by nanocrystalline Si [3].
Research supported by the European Commission, Horizon2020 FET- Open project PhENOMEN (Grant Agreement 713450).
[1] M.F. Colombano, G. Arregui, N.E. Capuj, A. Pitanti, J. Maire, A. Griol, B. Garrido, A. Martinez, C.M. Sotomayor Torres and D. Navarro-Urrios, "Synchronisation of optomechanical nanobeams by mechanical interaction", Physical Review Letters 123, 017402 (2019).
[2] G. Arregui, M.F. Colombano, J. Maire, A. Pitanti, N.E. Capuj, A. Griol, A. Martinez, C.M. Sotomayor-Torres and D. Navarro-Urrios, "Injection locking in an optomechanical coherent phonon source", accepted, Nanophotonics, https://doi.org/10.1515/nanoph-2020-0592
[3] D. Navarro Urrios, M. Colombano, J. Maire, E. Chavez-Angel, G. Arregui, N.E. Capuj , A. Devos, A. Griol, L. Bellieres, A. Martinez, K. Grigoras, T. Hakkinen, J. Saarilahti, T. Makkonen, C. M. Sotomayor Torres and J. Ahopelto, "Properties of Nanocrystalline Silicon probed by Optomechanics", Nanophotonics 9 (16) 4819 (2020); J Maire et al, in preparation.
Irrespective of the type of the carrier, thermal conductance via a ballistic channel is given by the quantum of thermal conductance. In this talk I present how this phenomenon realizes for thermal microwave photons in electrical circuits at low temperatures. I briefly review the circuit theoretical model, early experiments on the effect, and more recent experiments of my research group where the heat transport is controlled by superconducting qubits. These qubits can work as the working substance for heat valves and rectifiers and eventually for heat engines and refrigerators.
Controlling acoustic phonon spectrum at nanoscale is important for applications ranging from energy conversion to quantum computing. In many proposed implementations of a quantum computer, phonons limit the coherence of the state variables used for information encoding. Fine-tuning of acoustic phonon energy spectrum and group velocities can help in altering the electron - phonon and magnon - phonon coupling. In this presentation, I will review some of our recent results pertinent to the phonon spectrum engineering: Brillouin spectroscopy demonstration of the acoustic phonon confinement effects in individual semiconductor nanowires; modification of the acoustic phonon spectrum via incorporation of the size dissimilar dopant atoms; Raman spectroscopy measurements of the spin - lattice coupling; and the phonon folding in two-dimensional van der Waals materials induced by the atomic-layer twisting. The applications of the results to the thermal and quantum regimes will be discussed.
This work was supported, in part, by DOE EFRC SHINES at UC Riverside, NSF 2DARE, NSF DMREF and DARPA.
Active thermal management devices often lack the efficacy and energy efficiency of electronic switches. This is mainly because of the bosonic nature of phonons and the type of interactions they have with external forces. As a result, discovery of materials with unique vibrational properties that provide better control of thermal carriers is necessary. Our research shows that the phonons in group IVB transition metal dichalcogenides such as hafnium disulfide have distinct characteristics and provide remarkable mechanism for control of thermal careers. This is caused by the intermixing of van der Waals forces and covalent bonds in the material structure combined with their highly anisotropic bond properties. In this talk we present our results on vibrational and thermal transport properties of a member of this group, hafnium disulfide (HfS2). The highly asymmetric bond properties in HfS2 dominate the structure and vibrational properties of this material. We explore the physics of HfS2 by developing a comprehensive computational model to study its phonon behavior, anharmonic properties, and phonon transport characteristics. Our findings demonstrate a unique phonon behavior in the material where the absence of a phonon-gap between the acoustic and optical branches grant a more prominent and unique role to the optical modes of HfS2. As a result HfS2 has a low thermal conductivity, ranging between 0.3-5 W/mK. In additional only one acoustic phonon branch, the ZA branch, contributes up to 80% to the thermal transport of the material in both out-of-plane and in-plane crystal orientations. Our experiments confirm and support the theory and add further insight into an anomalous behavior in the optical modes. Our quasi-harmonic model reveals a structural phase transformation at around room temperature that leads to unique anharmonicity, discernible in the experimental results of the zone center out-of-plane optical mode. This unique phase transformation contributes to both changes in the phonon decay properties and thermal transport behavior. The structural phase transformation combined with the constricted ZA branch phonon carriers and the distinct scattering physics in optical branches of HfS2 provide unique means for control of thermal transport. We explore a few strategies for control of thermal properties in HfS2 based on fundamental vibrational properties of the material. We demonstrate that a successful approach for dynamic control of thermal conductivity is the control of van der Waals gap properties. We demonstrate that through intercalation and modification of these gaps a 4-fold control of cross-plane thermal conductivity in hafnium disulfide from 0.35 W/m-K to 1.45 W/m-K is achievable. We also demonstrate that an out-of-plane strain can be used to make thermal regulators based on HfS2. This research unveils a unique class of 2D layers with vibrational properties suitable for development of thermal management devices.
Phonon transport is the dominant mechanism of thermal conduction in most solids and has been studied for decades. A good understanding on many transport regimes in micro- and nanostructures could be established, including ballistic and diffusive transport, mode softening, or band structure engineering in phononic crystals. However, the limit of quantized transport and the engineering of single transport channels is much less explored. Here, we first review some concepts, theoretical and experimental progress in the field. Then examples from our own, ongoing work are given, showing thermal conductance quantization in single-atom contacts and single molecule junctions.
We acknowledge funding by the European Commission H2020-FETOPEN projects "EFINED" Grant Agreement number 766853, and "QuIET", Grant Agreement number 767187.
Localized heating and hot spots limit the operation of many electronic, optoelectronic and integrated acoustic devices. We describe various approaches to engineer heat flow with the use of ultra low or ultra high thermal conductivity materials. Deviations from Fourier heat diffusion manifest through quasi ballistic effects. We show that super diffusive and hydrodynamic heat flow could dominate temperature profile of submicron or ultrafast devices at room temperature. Challenges and opportunities in engineering heat flow will be highlighted.
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